Chitin is a linear polysaccharide composed of .beta.-(1-4)-linked 2-acetamido-2-deoxy-D-glucose units that occurs naturally in the exoskeleton of invertebrates, in particular the carapace of marine crustaceans. Chemical deacetylation of chitin yields chitosan which is a copolymer of 2-amino-2-deoxy-D-glucose and 2-acetamido-2-deoxy-D-glucose units. Chitosan has numerous uses including: an absorbent useful in water purification; a paper wet web strength enhancer; a blood cholesterol lowering compound; a compound useful in adjusting viscosity; a cosmetics additive; a pharmaceutical adjuvant and a dietary supplement.
With respect to the use of chitosan as a water-purifying agent, chitosan is known to bind numerous pollutants of aqueous systems, such as lakes and streams. For example, chitosan has the ability to bind heavy metals and certain halogenated, organic xenobiotics, such as PCPs (pentachlorophenols) and PCBs (polychlorinated biphenyls). Additionally, chitosan complexed with molybdenum is capable of binding orthophosphate ions which pollute lakes and streams. A chitosan preparation having a high density is especially desirable because it will more rapidly sink to the bottom of the body of water to which it is added, thereby sequestering bound contaminants, such as heavy metals, from the bulk of the water. The bound contaminants may therefore be more easily removed from the contaminated, aqueous system.
With respect to the use of chitosan as a dietary supplement, chitosan is often used to reduce the blood serum level of cholesterol, and to promote weight loss by impeding dietary fat absorption in the gastrointestinal tract. Chitosan can be encapsulated or tabletized either alone or in combination with other ingredients including vitamins C, E, B6, .beta.-carotene, folic acid, and a variety of binders. For the benefit of those individuals who have difficulty swallowing tablets or capsules, chitosan can be added to baked goods, such as crackers, cookies and cakes, and to beverages. Again, a high density preparation of chitosan is desirable because, for example, a smaller volume of high density chitosan need be consumed, compared to standard, lower density chitosan, in order to deliver the same dose of chitosan. Thus, for example, a person need consume fewer tablets or capsules of high density chitosan compared to standard preparations of lower density chitosan.
Chitosan is typically utilized in the form of a powder. A problem associated with powdered chitosan, however, is that it has poor flow characteristics as measured by its ability to pass through a narrow orifice without "bridging", i.e., without binding to form a plug within the orifice, thereby stopping flow. These poor flow characteristics make it difficult to handle and dispense large quantities of powdered chitosan. Also, these poor flow characteristics make it difficult to accurately and reproducibly dispense a standard amount of chitosan into, for example, a capsule.
There is therefore a need for a chitosan preparation having improved flow characteristics. Typically, chitosan preparations having increased density also have improved flow characteristics. An art recognized means for increasing the density, and thereby improving the flow characteristics, of powdered chitosan is to "slug" the chitosan powder by wetting the chitosan with water, roller pressing the wet chitosan, drying and regrinding. This process increases the bulk density of the chitosan, i.e., the weight of a chitosan sample divided by its non-packed volume. "Slugging" does not, however, substantially increase the tap density of the chitosan, i.e., the weight of a chitosan sample divided by its packed volume. In other words, "slugging" does not permit substantially more chitosan to be packed into a container, such as a capsule, of constant volume.
Consequently, there is a need for chitosan having high tap density and favorable flow characteristics, and for a process for making the same. Further, there is a need for a high tap density chitosan that has a reduced fish odor compared to the fish odor of existing, low tap density chitosans. A high tap density chitosan having a reduced fish odor is especially desirable for use as a dietary supplement.